An ectopic in vivo preparation, in which anterior pituitary tissue is transplanted into the hamster cheek pouch, will be used to study the differentiation of and regulation of pituitary hormone secretion. Studies will include determining the roles of the microcirculation and immune system in these two processes. Concurrent staining of releasing hormone (GnRH, TRH, SRIH, other) -secreting cells and aminergic neurons is proposed, using brains of rats and hamsters. Such a method would provide both identification and cytoarchitectural analysis of specific aminergic systems involved in specific pituitary secretory response patterns. In view of current hypotheses regarding the dual or multiple releasing activities of known releasing and release-inhibiting hormones (RH's) according to which selective anterior pituitary responses require permutative release of two or more RH's, special effort will be made to determine whether any aminergic neurons can be found to have synaptic junctions with more than one type of RH cell. Previously identified neuroendocrine structures will be tansplanted into the hamster cheek pouch, and used to study the microcirculation of neuroendocrine structures via transillumination. Special attention will be given to determining whether specific trans-capillary transport exists for feedback agents (both "loop-loop" and "short-loop") in the parenchyma of the central nervous system. Other studies will include determining the response of these vessels to vasoactive substances and hormones and the permeability of these vessels to metabolites, hormones, etc. in the presence of varying amounts of regulatory agents.